1. Field of the Invention
This invention generally relates to a filter aid for removing contaminants from water-based fluids used in metal working processes, as well as a method of using the same.
2. Background Information
Metal working fluids are commonly used for purposes of cooling, lubricating and/or cleaning metal during metal working processes such as cutting, grinding, forming, rolling, and the like. Fluids used for such purposes generally include petroleum derived compositions, oil-in-water emulsions, non-petroleum water soluble (synthetic) compositions, and synthetic emulsions, or combinations thereof Emulsified oil-in-water type metal working fluids typically comprise about 1-10% by weight of lubricants in combination with a small amount of an emulsifier, such as hydrogenated animal fat, sodium sulfonate complexes and the like, and about 90% or more by weight of water. Synthetic metal working fluids on the other hand typically comprise mixtures of a water miscible organic polymer in combination with borates and suitable wetting agents. As used herein, unless otherwise specifically noted, the term “metal working fluid” refers to oil-in-water emulsions that contain various combinations of water, emulsified oils, and other synthetic compositions.
Depending upon the particular metal working process, the metal working fluids typically become contaminated over a period of time with foreign matter such as metal particles (ferrous or non-ferrous), tramp oil, dirt, bacteria, and other foreign matter. For example, during the manufacturing of two-piece aluminum containers, e.g., beverage cans, a metal working fluid is continuously circulated within the can forming machinery in order to cool the forming tools used therein, provide lubrication, and to carry off unwanted waste aluminum particles. For economical reasons, this metal working fluid is continuously recirculated through the can forming machines. However, the metal working fluid gradually becomes contaminated with the waste aluminum particulates, tramp oil, and other contaminants. These contaminates are detrimental to the can forming process and the machinery used therewith, and thus the metal working fluid must be filtered in order to remove the contaminants.
For example, a liquid filtering device (such as that described in U.S. Pat. No. 3,608,734) is typically used to filter the recirculated metal working fluid. In this device, the contaminated metal working fluid is furnished to an input chamber located on the upstream side of a support structure that has a filter media supported thereon (such as that described in U.S. Pat. No. 4,925,560). The metal working fluid passes through the filter media and support structure to a collection chamber on the downstream side of the filter sheet. Contaminants in the coolant are collected in the filter media and clean metal working fluid is accumulated in collection chamber. Before and during the filtering process, a filter aid material (such as sawdust, wood pulp, or other cellulosic material) is added to and mixed with the contaminated metal working fluid in order to build up a cake on the filter media to enhance the filtering process.
Although the combination of the filter aid material and the filter media can successfully remove some of the contaminants in the metal working fluid, it is still quite porous and thus will allow smaller metal particles to pass therethrough. Thus, despite this filtration, this metal working fluid will change from a clear to opaque color to a dark gray color after 24 to 48 hours of use as it becomes more and more contaminated. This contamination, particularly the smaller metal particles that remain in the metal working fluid, can have a quite deleterious effect on the machinery in which it is used.
For example, in the aluminum beverage can forming machine noted above, aluminum particles generated during can making operations are generally between approximately 0.1 to 5 microns in diameter, but a conventional filter sheet used to remove these aluminum particles has an average pore size of approximately 5 to 20 microns. Even if a cake of the filter aid material is formed on the filter sheet, the average pore size of the filter will still be between approximately 2.5 to 5.0 microns. However, this reduced pore size will usually only be present during the last 20% of the filter cycle. Thus, a significant amount of the aluminum particles in the metal working fluid will simply pass through the filter, will cause premature wear in the moving parts in the machine, and both shorten the useful life of these parts and increase operating costs.
In addition, in the aforementioned aluminum beverage can forming machine, microscopic droplets of tramp oil in the metal working fluid will also pass through the filter, and adhere to the beverage cans produced by the can machine. This of course is highly undesirable as it increases costs associated with cleaning the cans.
Furthermore, although the use of the aforementioned filter aid material enhances the filtering process, it has a drawback in that the filter will eventually become clogged after the filter aid material becomes saturated with metal particles, tramp oil, and other contaminates. This of course requires the filter to be frequently replaced, which in turn will increase operating costs.
There have been some efforts in the past to address these problems with respect to aqueous fluids (i.e., solutions that are not oil-in-water emulsions), and also with respect to non-aqueous fluids (e.g., solutions composed primarily of petroleum-based lubricants).
For example, U.S. Pat. No. 4,177,142 (the '142 patent) discloses a filter bed composed of a mixture of cellulose fibers and a cationic organic polyelectrolyte, and a method of using the same. This reference states that this combination shows effectiveness in removing iron oxide from an aqueous fluid, and also states that that this combination reduces the pressure drop across the filter and increases filtration efficiency due to the “clumping” phenomenon. This reference states that the “clumping” phenomenon occurs because the cellulose fibers and the cationic organic polyelectrolyte have opposite electric charges, and thus agglomerate together to form larger particles when in aqueous solution. When these larger particles are formed into a filter bed, a greater void space (pore size) is created between the particles in the filter bed and thus aqueous fluids can more readily pass through the filter bed. However, although the '142 patent teaches that a cationic organic polyelectrolyte can be used to produce the “clumping” phenomenon, it is clear that this cannot include all cationic organic polyelectrolytes known in the art because not all of these compounds will produce a “clumping” phenomenon when combined with cellulose fibers in all types of liquids. For example, some cationic organic polyelectrolytes will clump in an aqueous environment, but will not clump in an oil-in-water emulsion. Furthermore, it should be noted that the '142 patent is silent with respect to the use of the combination of cellulose fibers and a cationic organic polyelectrolyte to filter oil-in-water emulsions contaminated with metal particles. Indeed, it has long been believed by those of ordinary skill in the art that this combination would be unacceptable for use as a filter to remove metal particles, tramp oil, and other contaminants from an oil-in-water emulsion. This is because it was believed that the oil in the oil-in-water emulsion would quickly clog the filter, and thus eliminate any improvement in pressure drop and filtration efficiency that the invention in the '142 patent provided.
In addition, U.S. Pat. No. 5,154,828 (the '828 patent) discloses a filter aid material composed of cellulose fibers treated with an acid material for reclaiming and maintaining a coolant oil (i.e., a non-aqueous fluid) used in aluminum rolling or working processes, and a process for using the same. This reference states that this combination shows effectiveness in removing aluminum oxide from a non-aqueous fluid. However, the '828 patent is silent with respect to the use of the combination of cellulose fibers and an acid material to filter oil-in-water emulsions contaminated with metal particles. Indeed, it has long been believed by those of ordinary skill in the art that this combination would be unacceptable for use in an oil-in-water emulsion because the acid material would quickly leach out of the cellulose fibers due to the presence of water, and thus prevent the slow, controlled reaction between the aluminum and the acid material described as critical in the '828 patent.
In view of the above, there exists a need for a filter aid material and a method of using the same which overcomes the above mentioned problems in the prior art. This invention addresses this need in the prior art as well as other needs, which will become apparent to those skilled in the art from this disclosure.